Electro-optic displays, and materials and methods for production thereof

ABSTRACT

An electro-optic display is produced using a sub-assembly comprising a front sheet, an electro-optic medium; and an adhesive layer. An aperture is formed through the adhesive layer where the adhesive layer is not covered by the electro-optic medium, and the sub-assembly is adhered to a backplane having a co-operating member with the aperture engaged with a co-operating member, thus locating the sub-assembly relative to the backplane. In another form of electro-optic display, a chip extends through an aperture in the electro-optic medium and adhesive layer. In a third form, the aforementioned sub-assembly is secured to a backplane and then a cut is made through both backplane and sub-assembly to provide an aligned edge.

REFERENCE TO RELATED APPLICATIONS

This application is a division of copending application Ser. No.13/208,916, filed Aug. 12, 2011 (Publication No. 2011/0297309), which isitself a division of application Ser. No. 12/147,571 filed Jun. 27, 2008(Publication No. 2009/0000729, now U.S. Pat. No. 8,034,209, issued Oct.11, 2011), which claims benefit of copending Application Ser. No.60/947,039, filed Jun. 29, 2007.

This invention is also related to:

-   -   (a) U.S. Pat. No. 6,982,178;    -   (b) copending application Ser. No. 10/605,024, filed Sep. 2,        2003 (Publication No. 2004/0155857, now U.S. Pat. No.        7,561,324), which claims benefit of Application Ser. No.        60/319,516, filed Sep. 3, 2002;    -   (c) U.S. Pat. No. 7,110,164;    -   (d) U.S. Pat. No. 7,075,703;    -   (e) U.S. Patent Publication No. 2007/0109219, now U.S. Pat. No.        7,839,564;    -   (f) U.S. Patent Publication No. 2007/0152956, now U.S. Pat. No.        7,649,674;    -   (g) U.S. Patent Publication No. 2007/0211331, now U.S. Pat. No.        7,733,554; and    -   (h) U.S. Patent Publication No. 2008/0057252, now U.S. Pat. No.        7,583,427.

The entire contents of these copending applications, publications andpatents, and of all other U.S. patents and published and copendingapplications mentioned below, are herein incorporated by reference.

BACKGROUND OF INVENTION

This invention relates to electro-optic displays, and to materials andmethods for the production of such displays. This invention isparticularly, but not exclusively, intended for use with displayscomprising encapsulated electrophoretic media. However, the inventioncan also make use of various other types of electro-optic media whichare solid, in the sense that they have solid external surfaces, althoughthe media may, and often do, have internal cavities which contain afluid (either liquid or gas). Thus, the term “solid electro-opticdisplays” includes encapsulated electrophoretic displays, encapsulatedliquid crystal displays, and other types of displays discussed below.

Electro-optic displays comprise a layer of electro-optic material, aterm which is used herein in its conventional meaning in the imaging artto refer to a material having first and second display states differingin at least one optical property, the material being changed from itsfirst to its second display state by application of an electric field tothe material. Although the optical property is typically colorperceptible to the human eye, it may be another optical property, suchas optical transmission, reflectance, luminescence or, in the case ofdisplays intended for machine reading, pseudo-color in the sense of achange in reflectance of electromagnetic wavelengths outside the visiblerange.

The terms “bistable” and “bistability” are used herein in theirconventional meaning in the art to refer to displays comprising displayelements having first and second display states differing in at leastone optical property, and such that after any given element has beendriven, by means of an addressing pulse of finite duration, to assumeeither its first or second display state, after the addressing pulse hasterminated, that state will persist for at least several times, forexample at least four times, the minimum duration of the addressingpulse required to change the state of the display element. It is shownin U.S. Pat. No. 7,170,670 that some particle-based electrophoreticdisplays capable of gray scale are stable not only in their extremeblack and white states but also in their intermediate gray states, andthe same is true of some other types of electro-optic displays. Thistype of display is properly called “multi-stable” rather than bistable,although for convenience the term “bistable” may be used herein to coverboth bistable and multi-stable displays.

Several types of electro-optic displays are known. One type ofelectro-optic display is a rotating bichromal member type as described,for example, in U.S. Pat. Nos. 5,808,783; 5,777,782; 5,760,761;6,054,071 6,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791(although this type of display is often referred to as a “rotatingbichromal ball” display, the term “rotating bichromal member” ispreferred as more accurate since in some of the patents mentioned abovethe rotating members are not spherical). Such a display uses a largenumber of small bodies (typically spherical or cylindrical) which havetwo or more sections with differing optical characteristics, and aninternal dipole. These bodies are suspended within liquid-filledvacuoles within a matrix, the vacuoles being filled with liquid so thatthe bodies are free to rotate. The appearance of the display is changedby applying an electric field thereto, thus rotating the bodies tovarious positions and varying which of the sections of the bodies isseen through a viewing surface. This type of electro-optic medium istypically bistable.

Another type of electro-optic display uses an electrochromic medium, forexample an electrochromic medium in the form of a nanochromic filmcomprising an electrode formed at least in part from a semi-conductingmetal oxide and a plurality of dye molecules capable of reversible colorchange attached to the electrode; see, for example O'Regan, B., et al.,Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24(March 2002). See also Bach, U., et al., Adv. Mater., 2002, 14(11), 845.Nanochromic films of this type are also described, for example, in U.S.Pat. Nos. 6,301,038; 6,870,657; and 6,950,220. This type of medium isalso typically bistable.

Another type of electro-optic display is an electro-wetting displaydeveloped by Philips and described in Hayes, R. A., et al., “Video-SpeedElectronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003).It is shown in copending application Ser. No. 10/711,802, filed Oct. 6,2004 (Publication No. 2005/0151709), that such electro-wetting displayscan be made bistable.

Another type of electro-optic display, which has been the subject ofintense research and development for a number of years, is theparticle-based electrophoretic display, in which a plurality of chargedparticles move through a fluid under the influence of an electric field.Electrophoretic displays can have attributes of good brightness andcontrast, wide viewing angles, state bistability, and low powerconsumption when compared with liquid crystal displays. Nevertheless,problems with the long-term image quality of these displays haveprevented their widespread usage. For example, particles that make upelectrophoretic displays tend to settle, resulting in inadequateservice-life for these displays.

As noted above, electrophoretic media require the presence of a fluid.In most prior art electrophoretic media, this fluid is a liquid, butelectrophoretic media can be produced using gaseous fluids; see, forexample, Kitamura, T., et al., “Electrical toner movement for electronicpaper-like display”, IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y.,et al., “Toner display using insulative particles chargedtriboelectrically”, IDW Japan, 2001, Paper AMD4-4). See also U.S. PatentPublication Nos. 2005/0259068, 2006/0087479, 2006/0087489, 2006/0087718,2006/0209008, 2006/0214906, 2006/0231401, 2006/0238488, 2006/0263927 andU.S. Pat. Nos. 7,321,459 and 7,236,291. Such gas-based electrophoreticmedia appear to be susceptible to the same types of problems due toparticle settling as liquid-based electrophoretic media, when the mediaare used in an orientation which permits such settling, for example in asign where the medium is disposed in a vertical plane. Indeed, particlesettling appears to be a more serious problem in gas-basedelectrophoretic media than in liquid-based ones, since the lowerviscosity of gaseous suspending fluids as compared with liquid onesallows more rapid settling of the electrophoretic particles.

Numerous patents and applications assigned to or in the names of theMassachusetts Institute of Technology (MIT) and E Ink Corporation haverecently been published describing encapsulated electrophoretic media.Such encapsulated media comprise numerous small capsules, each of whichitself comprises an internal phase containing electrophoretically-mobileparticles suspended in a liquid suspending medium, and a capsule wallsurrounding the internal phase. Typically, the capsules are themselvesheld within a polymeric binder to form a coherent layer positionedbetween two electrodes. Encapsulated media of this type are described,for example, in U.S. Pat. Nos. 5,930,026; 5,961,804; 6,017,584;6,067,185; 6,118,426; 6,120,588; 6,120,839; 6,124,851; 6,130,773;6,130,774; 6,172,798; 6,177,921; 6,232,950; 6,249,271; 6,252,564;6,262,706; 6,262,833; 6,300,932; 6,312,304; 6,312,971; 6,323,989;6,327,072; 6,376,828; 6,377,387; 6,392,785; 6,392,786; 6,413,790;6,422,687; 6,445,374; 6,445,489; 6,459,418; 6,473,072; 6,480,182;6,498,114; 6,504,524; 6,506,438; 6,512,354; 6,515,649; 6,518,949;6,521,489; 6,531,997; 6,535,197; 6,538,801; 6,545,291; 6,580,545;6,639,578; 6,652,075; 6,657,772; 6,664,944; 6,680,725; 6,683,333;6,704,133; 6,710,540; 6,721,083; 6,724,519; 6,727,881; 6,738,050;6,750,473; 6,753,999; 6,816,147; 6,819,471; 6,822,782; 6,825,068;6,825,829; 6,825,970; 6,831,769; 6,839,158; 6,842,167; 6,842,279;6,842,657; 6,864,875; 6,865,010; 6,866,760; 6,870,661; 6,900,851;6,922,276; 6,950,200; 6,958,848; 6,967,640; 6,982,178; 6,987,603;6,995,550; 7,002,728; 7,012,600; 7,012,735; 7,023,420; 7,030,412;7,030,854; 7,034,783; 7,038,655; 7,061,663; 7,071,913; 7,075,502;7,075,703; 7,079,305; 7,106,296; 7,109,968; 7,110,163; 7,110,164;7,116,318; 7,116,466; 7,119,759; 7,119,772; 7,148,128; 7,167,155;7,170,670; 7,173,752; 7,176,880; 7,180,649; 7,190,008; 7,193,625;7,202,847; 7,202,991; 7,206,119; 7,223,672; 7,230,750; 7,230,751;7,236,790; 7,236,792; 7,242,513; 7,247,379; 7,256,766; 7,259,744;7,280,094; 7,304,634; 7,304,787; 7,312,784; 7,312,794; 7,312,916;7,237,511; 7,339,715; 7,349,148; 7,352,353; 7,365,394; and 7,365,733;and U.S. Patent Applications Publication Nos. 2002/0060321;2002/0090980; 2003/0102858; 2003/0151702; 2003/0222315; 2004/0105036;2004/0112750; 2004/0119681; 2004/0155857; 2004/0180476; 2004/0190114;2004/0257635; 2004/0263947; 2005/0000813; 2005/0007336; 2005/0012980;2005/0018273; 2005/0024353; 2005/0062714; 2005/0099672; 2005/0122284;2005/0122306; 2005/0122563; 2005/0134554; 2005/0151709; 2005/0152018;2005/0156340; 2005/0179642; 2005/0190137; 2005/0212747; 2005/0253777;2005/0280626; 2006/0007527; 2006/0038772; 2006/0139308; 2006/0139310;2006/0139311; 2006/0176267; 2006/0181492; 2006/0181504; 2006/0194619;2006/0197737; 2006/0197738; 2006/0202949; 2006/0223282; 2006/0232531;2006/0245038; 2006/0262060; 2006/0279527; 2006/0291034; 2007/0035532;2007/0035808; 2007/0052757; 2007/0057908; 2007/0069247; 2007/0085818;2007/0091417; 2007/0091418; 2007/0109219; 2007/0128352; 2007/0146310;2007/0152956; 2007/0153361; 2007/0200795; 2007/0200874; 2007/0201124;2007/0207560; 2007/0211002; 2007/0211331; 2007/0223079; 2007/0247697;2007/0285385; 2007/0286975; 2007/0286975; 2008/0013155; 2008/0013156;2008/0023332; 2008/0024429; 2008/0024482; 2008/0030832; 2008/0043318;2008/0048969; 2008/0048970; 2008/0054879; 2008/0057252; and2008/0074730; and International Applications Publication Nos. WO00/38000; WO 00/36560; WO 00/67110; and WO 01/07961; and EuropeanPatents Nos. 1,099,207 B1; and 1,145,072 B1.

Many of the aforementioned patents and applications recognize that thewalls surrounding the discrete microcapsules in an encapsulatedelectrophoretic medium could be replaced by a continuous phase, thusproducing a so-called polymer-dispersed electrophoretic display, inwhich the electrophoretic medium comprises a plurality of discretedroplets of an electrophoretic fluid and a continuous phase of apolymeric material, and that the discrete droplets of electrophoreticfluid within such a polymer-dispersed electrophoretic display may beregarded as capsules or microcapsules even though no discrete capsulemembrane is associated with each individual droplet; see for example,the aforementioned U.S. Pat. No. 6,866,760. Accordingly, for purposes ofthe present application, such polymer-dispersed electrophoretic mediaare regarded as sub-species of encapsulated electrophoretic media.

A related type of electrophoretic display is a so-called “microcellelectrophoretic display”. In a microcell electrophoretic display, thecharged particles and the fluid are not encapsulated withinmicrocapsules but instead are retained within a plurality of cavitiesformed within a carrier medium, typically a polymeric film. See, forexample, U.S. Pat. Nos. 6,672,921 and 6,788,449, both assigned to SipixImaging, Inc.

Although electrophoretic media are often opaque (since, for example, inmany electrophoretic media, the particles substantially blocktransmission of visible light through the display) and operate in areflective mode, many electrophoretic displays can be made to operate ina so-called “shutter mode” in which one display state is substantiallyopaque and one is light-transmissive. See, for example, theaforementioned U.S. Pat. Nos. 6,130,774 and 6,172,798, and U.S. Pat.Nos. 5,872,552; 6,144,361; 6,271,823; 6,225,971; and 6,184,856.Dielectrophoretic displays, which are similar to electrophoreticdisplays but rely upon variations in electric field strength, canoperate in a similar mode; see U.S. Pat. No. 4,418,346. Other types ofelectro-optic displays may also be capable of operating in shutter mode.

An encapsulated electrophoretic display typically does not suffer fromthe clustering and settling failure mode of traditional electrophoreticdevices and provides further advantages, such as the ability to print orcoat the display on a wide variety of flexible and rigid substrates.(Use of the word “printing” is intended to include all forms of printingand coating, including, but without limitation: pre-metered coatingssuch as patch die coating, slot or extrusion coating, slide or cascadecoating, curtain coating; roll coating such as knife over roll coating,forward and reverse roll coating; gravure coating; dip coating; spraycoating; meniscus coating; spin coating; brush coating; air knifecoating; silk screen printing processes; electrostatic printingprocesses; thermal printing processes; ink jet printing processes;electrophoretic deposition (See U.S. Pat. No. 7,339,715); and othersimilar techniques.) Thus, the resulting display can be flexible.Further, because the display medium can be printed (using a variety ofmethods), the display itself can be made inexpensively.

Other types of electro-optic materials may also be used in the presentinvention.

An electro-optic display normally comprises a layer of electro-opticmaterial and at least two other layers disposed on opposed sides of theelectro-optic material, one of these two layers being an electrodelayer. In most such displays both the layers are electrode layers, andone or both of the electrode layers are patterned to define the pixelsof the display. For example, one electrode layer may be patterned intoelongate row electrodes and the other into elongate column electrodesrunning at right angles to the row electrodes, the pixels being definedby the intersections of the row and column electrodes. Alternatively,and more commonly, one electrode layer has the form of a singlecontinuous electrode and the other electrode layer is patterned into amatrix of pixel electrodes, each of which defines one pixel of thedisplay. In another type of electro-optic display, which is intended foruse with a stylus, print head or similar movable electrode separate fromthe display, only one of the layers adjacent the electro-optic layercomprises an electrode, the layer on the opposed side of theelectro-optic layer typically being a protective layer intended toprevent the movable electrode damaging the electro-optic layer.

The manufacture of a three-layer electro-optic display normally involvesat least one lamination operation. For example, in several of theaforementioned MIT and E Ink patents and applications, there isdescribed a process for manufacturing an encapsulated electrophoreticdisplay in which an encapsulated electrophoretic medium comprisingcapsules in a binder is coated on to a flexible substrate comprisingindium tin oxide (ITO) or a similar conductive coating (which acts as anone electrode of the final display) on a plastic film, thecapsules/binder coating being dried to form a coherent layer of theelectrophoretic medium firmly adhered to the substrate. Separately, abackplane, containing an array of pixel electrodes and an appropriatearrangement of conductors to connect the pixel electrodes to drivecircuitry, is prepared. To form the final display, the substrate havingthe capsule/binder layer thereon is laminated to the backplane using alamination adhesive. (A very similar process can be used to prepare anelectrophoretic display usable with a stylus or similar movableelectrode by replacing the backplane with a simple protective layer,such as a plastic film, over which the stylus or other movable electrodecan slide.) In one preferred form of such a process, the backplane isitself flexible and is prepared by printing the pixel electrodes andconductors on a plastic film or other flexible substrate. The obviouslamination technique for mass production of displays by this process isroll lamination using a lamination adhesive. Similar manufacturingtechniques can be used with other types of electro-optic displays. Forexample, a microcell electrophoretic medium or a rotating bichromalmember medium may be laminated to a backplane in substantially the samemanner as an encapsulated electrophoretic medium.

As discussed in the aforementioned U.S. Pat. No. 6,982,178, (see column3, lines 63 to column 5, line 46) many of the components used in solidelectro-optic displays, and the methods used to manufacture suchdisplays, are derived from technology used in liquid crystal displays(LCD's), which are of course also electro-optic displays, though using aliquid rather than a solid medium. For example, solid electro-opticdisplays may make use of an active matrix backplane comprising an arrayof transistors or diodes and a corresponding array of pixel electrodes,and a “continuous” front electrode (in the sense of an electrode whichextends over multiple pixels and typically the whole display) on atransparent substrate, these components being essentially the same as inLCD's. However, the methods used for assembling LCD's cannot be usedwith solid electro-optic displays. LCD's are normally assembled byforming the backplane and front electrode on separate glass substrates,then adhesively securing these components together leaving a smallaperture between them, placing the resultant assembly under vacuum, andimmersing the assembly in a bath of the liquid crystal, so that theliquid crystal flows through the aperture between the backplane and thefront electrode. Finally, with the liquid crystal in place, the apertureis sealed to provide the final display.

This LCD assembly process cannot readily be transferred to solidelectro-optic displays. Because the electro-optic material is solid, itmust be present between the backplane and the front electrode beforethese two integers are secured to each other. Furthermore, in contrastto a liquid crystal material, which is simply placed between the frontelectrode and the backplane without being attached to either, a solidelectro-optic medium normally needs to be secured to both; in most casesthe solid electro-optic medium is formed on the front electrode, sincethis is generally easier than forming the medium on thecircuitry-containing backplane, and the front electrode/electro-opticmedium combination is then laminated to the backplane, typically bycovering the entire surface of the electro-optic medium with an adhesiveand laminating under heat, pressure and possibly vacuum. Accordingly,most prior art methods for final lamination of solid electrophoreticdisplays are essentially batch methods in which (typically) theelectro-optic medium, a lamination adhesive and a backplane are broughttogether immediately prior to final assembly, and it is desirable toprovide methods better adapted for mass production.

Electro-optic displays are often costly; for example, the cost of thecolor LCD found in a portable computer is typically a substantialfraction of the entire cost of the computer. As the use of electro-opticdisplays spreads to devices, such as cellular telephones and personaldigital assistants (PDA's), much less costly than portable computers,there is great pressure to reduce the costs of such displays. Theability to form layers of some solid electro-optic media by printingtechniques on flexible substrates, as discussed above, opens up thepossibility of reducing the cost of electro-optic components of displaysby using mass production techniques such as roll-to-roll coating usingcommercial equipment used for the production of coated papers, polymericfilms and similar media.

The aforementioned U.S. Pat. No. 6,982,178 describes a method ofassembling a solid electro-optic display (including an encapsulatedelectrophoretic display) which is well adapted for mass production.Essentially, this patent describes a so-called “front plane laminate”(“FPL”) which comprises, in order, a light-transmissiveelectrically-conductive layer; a layer of a solid electro-optic mediumin electrical contact with the electrically-conductive layer; anadhesive layer; and a release sheet. Typically, the light-transmissiveelectrically-conductive layer will be carried on a light-transmissivesubstrate, which is preferably flexible, in the sense that the substratecan be manually wrapped around a drum (say) 10 inches (254 mm) indiameter without permanent deformation. The term “light-transmissive” isused in this patent and herein to mean that the layer thus designatedtransmits sufficient light to enable an observer, looking through thatlayer, to observe the change in display states of the electro-opticmedium, which will normally be viewed through theelectrically-conductive layer and adjacent substrate (if present); incases where the electro-optic medium displays a change in reflectivityat non-visible wavelengths, the term “light-transmissive” should ofcourse be interpreted to refer to transmission of the relevantnon-visible wavelengths. The substrate will typically be a polymericfilm, and will normally have a thickness in the range of about 1 toabout 25 mil (25 to 634 μm), preferably about 2 to about 10 mil (51 to254 μm). The electrically-conductive layer is conveniently a thin metalor metal oxide layer of, for example, aluminum or ITO, or may be aconductive polymer. Poly(ethylene terephthalate) (PET) films coated withaluminum or ITO are available commercially, for example as “aluminizedMylar” (“Mylar” is a Registered Trade Mark) from E.I. du Pont de Nemours& Company, Wilmington Del., and such commercial materials may be usedwith good results in the front plane laminate.

The aforementioned U.S. Pat. No. 6,982,178 also describes a method fortesting the electro-optic medium in a front plane laminate prior toincorporation of the front plane laminate into a display. In thistesting method, the release sheet is provided with an electricallyconductive layer, and a voltage sufficient to change the optical stateof the electro-optic medium is applied between this electricallyconductive layer and the electrically conductive layer on the opposedside of the electro-optic medium. Observation of the electro-opticmedium will then reveal any faults in the medium, thus avoidinglaminating faulty electro-optic medium into a display, with theresultant cost of scrapping the entire display, not merely the faultyfront plane laminate.

The aforementioned U.S. Pat. No. 6,982,178 also describes a secondmethod for testing the electro-optic medium in a front plane laminate byplacing an electrostatic charge on the release sheet, thus forming animage on the electro-optic medium. This image is then observed in thesame way as before to detect any faults in the electro-optic medium.

Assembly of an electro-optic display using such a front plane laminatemay be effected by removing the release sheet from the front planelaminate and contacting the adhesive layer with the backplane underconditions effective to cause the adhesive layer to adhere to thebackplane, thereby securing the adhesive layer, layer of electro-opticmedium and electrically-conductive layer to the backplane. This processis well-adapted to mass production since the front plane laminate may bemass produced, typically using roll-to-roll coating techniques, and thencut into pieces of any size needed for use with specific backplanes.

The aforementioned 2004/0155857 describes a so-called “double releasefilm” which is essentially a simplified version of the front planelaminate of the aforementioned U.S. Pat. No. 6,982,178. One form of thedouble release sheet comprises a layer of a solid electro-optic mediumsandwiched between two adhesive layers, one or both of the adhesivelayers being covered by a release sheet. Another form of the doublerelease sheet comprises a layer of a solid electro-optic mediumsandwiched between two release sheets. Both forms of the double releasefilm are intended for use in a process generally similar to the processfor assembling an electro-optic display from a front plane laminatealready described, but involving two separate laminations; typically, ina first lamination the double release sheet is laminated to a frontelectrode to form a front sub-assembly, and then in a second laminationthe front sub-assembly is laminated to a backplane to form the finaldisplay, although the order of these two laminations could be reversedif desired.

The aforementioned 2007/0109219 describes a so-called “inverted frontplane laminate”, which is a variant of the front plane laminatedescribed in the aforementioned U.S. Pat. No. 6,982,178. This invertedfront plane laminate comprises, in order, at least one of alight-transmissive protective layer and a light-transmissiveelectrically-conductive layer; an adhesive layer; a layer of a solidelectro-optic medium; and a release sheet. This inverted front planelaminate is used to form an electro-optic display having a layer oflamination adhesive between the electro-optic layer and the frontelectrode or front substrate; a second, typically thin layer of adhesivemay or may not be present between the electro-optic layer and abackplane. Such electro-optic displays can combine good resolution withgood low temperature performance.

The aforementioned 2007/0109219 also describes various methods designedfor high volume manufacture of electro-optic displays using invertedfront plane laminates; preferred forms of these methods are “multi-up”methods designed to allow lamination of components for a plurality ofelectro-optic displays at one time.

The aforementioned U.S. Pat. No. 6,982,178 also describes methods forforming an electrical connection between a backplane to which the frontplane laminate is laminated and the light-transmissiveelectrically-conductive layer within the front plane laminate. Asillustrated in FIGS. 21 and 22 of this patent, the formation of thelayer of electro-optic medium within the front plane laminate may becontrolled so as to leave uncoated areas (“gutters”) where noelectro-optic medium is present, and portions of these uncoated areascan later serve to form the necessary electrical connections. However,this method of forming connections tends to be undesirable from amanufacturing point of view, since the placement of the connections isof course a function of the backplane design, so that FPL coated with aspecific arrangement of gutters can only be used with one, or a limitedrange of backplanes, whereas for economic reasons it is desirable toproduce only one form of FPL which can be used with any backplane.

Accordingly, the aforementioned U.S. Pat. No. 6,982,178 also describesmethods for forming the necessary electrical connections by coatingelectro-optic medium over the whole area of the FPL and then removingthe electro-optic medium where it is desired to form electricalconnections. However, such removal of electro-optic medium poses its ownproblems. Typically, the electro-optic medium must be removed by the useof solvents or mechanical cleaning, either of which may result in damageto, or removal of, the electrically-conductive layer of the FPL (thiselectrically-conductive layer usually being a layer of a metal oxide,for example indium tin oxide, less than 1 μm thick), causing a failedelectrical connection. In extreme cases, damage may also be caused tothe front substrate (typically a polymeric film) which is used tosupport and mechanically protect the conductive layer. In some cases,the materials from which the electro-optic medium is formed may not beeasily solvated, and it may not be possible to remove them without theuse of aggressive solvents and/or high mechanical pressures, either ofwhich will exacerbate the aforementioned problems.

Similar methods using selective coating of electro-optic medium and/orselective removal of electro-optic medium may also be applied to thedouble release films and inverted front plane laminates discussed above.

It is common practice to use laser cutting to separate from a continuousweb of FPL pieces of appropriate sizes for lamination to individualbackplanes. Such laser cutting can also be used to prepare areas forelectrical connections to the backplane by “kiss cutting” the FPL withthe laser from the lamination adhesive side so that the laminationadhesive and electro-optic medium are removed from the connection areas,but the electrically-conductive layer is not removed. Such kiss cuttingrequires accurate control of both laser power and cutting speed if thethin and relatively fragile electrically-conductive layer is not to beremoved or damaged. Also, depending upon the location of the connection,bending of the electrically-conductive layer and the associated frontsubstrate may crack the conductive layer, resulting in failure to make aproper connection between the backplane and the conductive layer, andhence display failure.

The aforementioned 2007/0211331 describes methods of forming electricalconnections to the conductive layers of front plane laminates. Thisapplication describes a first process for the production of a frontplane laminate which comprises forming a sub-assembly comprising a layerof lamination adhesive and a layer of electro-optic medium; forming anaperture through this sub-assembly; and thereafter securing to theexposed surface of the lamination adhesive a light-transmissiveelectrode layer extending across the aperture. The resultant FPL has apre-cut aperture through the electro-optic medium and adhesive layers,this pre-cut aperture allowing contact to be made with the electrodelayer.

The aforementioned 2007/0211331 also describes a second process for theproduction of a front plane laminate which comprises forming asub-assembly comprising a layer of lamination adhesive and a layer ofelectro-optic medium; and thereafter securing to the exposed surface ofthe lamination adhesive a light-transmissive electrode layer, theelectrode layer having a tab portion which extends beyond the peripheryof the lamination adhesive and electro-optic layers.

One area of electro-optic display manufacture which still presentproblems is aligning the FPL or similar front sub-assembly with thebackplane. As already noted, the FPL or other front sub-assembly isformed as a web or large sheet which must be cut to provide pieces ofappropriate size for formation of single displays. It is normallynecessary to ensure that the FPL or similar front sub-assembly piece isaccurately aligned with certain features of the backplane; for example,it may be necessary to ensure that an electrode layer in a FPL contactselectrical contacts present on the backplane. The present inventionprovides methods for facilitating such alignment. One form of thepresent invention is especially adapted for achieving a clean edgealignment between an FPL or similar front sub-assembly and a backplanesubstantially the same size as the front sub-assembly.

The present invention also provides a method to facilitate mounting ofdriver chips or other circuitry on the backplane of an electro-opticdisplay.

SUMMARY OF THE INVENTION

Accordingly, in one aspect this invention provides a process for theproduction of an electro-optic display, the process comprising:

-   -   forming a sub-assembly comprising in order, a front sheet; a        layer of electro-optic medium; and an adhesive layer, the        adhesive layer being larger in at least one dimension than the        layer of electro-optic material;    -   forming an aperture through the adhesive layer in an area where        the adhesive layer is not covered by the layer of electro-optic        medium;    -   bringing the sub-assembly having the aperture formed through the        adhesive layer adjacent a backplane comprising at least one        electrode and having at least one co-operating member associated        therewith, with the aperture engaged with a co-operating member,        thereby locating the sub-assembly relative to the backplane.

This process of the present invention may hereinafter for convenience becalled the “adhesive layer locating aperture” or “ALLA” process of theinvention.

In such an ALLA process, the front sheet may comprise alight-transmissive electrically-conductive layer which will form a frontelectrode in the final display, so that the sub-assembly has the form ofa FPL or inverted FPL. Also, in such a case, the front sheet willtypically also comprise at least one supporting or protective layer onthe opposed side of the electrically-conductive layer from the layer ofelectro-optic medium, the supporting or protective layer serving tosupport the electrically-conductive layer and to protect it againstmechanical damage. The supporting or protective layer may also serveother functions, for example by acting as a barrier against water vaporand/or ultra-violet radiation, and/or providing a desired surfacetexture. (The electro-optic medium is of course normally viewed from theside opposite to the backplane.) Alternatively, the front sheet maycomprise a second adhesive layer, typically covered by a release sheet,to permit later lamination of the layer of electro-optic medium to afront electrode and optionally other layers.

In the ALLA process, it is normally desirable to provide at least twolocating apertures to ensure that the sub-assembly cannot rotaterelative to the backplane and hence is unambiguously fixed in a knownposition relative to the backplane. It is not necessary that theco-operating member or members be physically located on the backplane;for example, the co-operating members could be provided on a supportmember, and both the backplane and the sub-assembly provided withapertures which engage the co-operating members on the support member,thereby locating the backplane and the sub-assembly in known positionsrelative to each other. When, as is typically the case, the sub-assemblyis formed as a web or sheet containing material for a plurality ofdisplays, the formation of the aperture through the adhesive layer isconveniently effected at the same time as the sub-assembly is dividedinto sections corresponding to individual displays. Also, in the ALLAprocess, typically, the adhesive layer is larger in both dimensions thanthe layer of electro-optic material.

In another aspect, this invention provides a process for the productionof an electro-optic display, the process comprising:

-   -   forming a sub-assembly comprising in order, a front sheet; a        layer of electro-optic medium; and an adhesive layer;    -   forming an aperture through the front sheet, layer of        electro-optic medium and adhesive layer;    -   securing the sub-assembly to a backplane comprising at least one        pixel electrode; and    -   mounting at least one electronic circuit device on the        backplane, the electronic circuit device extending through the        aperture in the sub-assembly.

This process of the present invention may hereinafter for convenience becalled the “chip in sub-assembly aperture” or “CSAR” process of theinvention.

In the CSSA, the electronic circuit device will typically be at leastpartially surrounded by a potting material. As is well known in theelectronics art, such a potting material can serve to protect bondsbetween the electronic circuit device and the backplane fromenvironmental contaminants and mechanically stabilize theinterconnections between the electronic circuit device and thebackplane. In a preferred form of the CSSA process, the potting materialcontains a portion of the sub-assembly adjacent the aperture.

In the CSSA process, as in the ALLA process, the front sheet maycomprise a light-transmissive electrically-conductive layer which willform a front electrode in the final display, so that the sub-assemblyhas the form of a FPL or inverted FPL. Also, in such a case, the frontsheet will typically also comprise at least one supporting or protectivelayer on the opposed side of the electrically-conductive layer from thelayer of electro-optic medium, the supporting or protective layerserving to support the electrically-conductive layer and to protect itagainst mechanical damage. The supporting or protective layer may alsoserve other functions, for example by acting as a barrier against watervapor and/or ultra-violet radiation, and/or providing a desired surfacetexture. Alternatively, the front sheet may comprise a second adhesivelayer, typically covered by a release sheet, to permit later laminationof the layer of electro-optic medium to a front electrode and optionallyother layers.

In another aspect, this invention provides a process for the productionof an electro-optic display, the process comprising:

-   -   forming a sub-assembly comprising in order, a front sheet; a        layer of electro-optic medium; and an adhesive layer;    -   securing the sub-assembly to a backplane comprising at least one        pixel electrode; and    -   cutting through both the sub-assembly and the backplane, thereby        removing peripheral portions of both the sub-assembly and the        backplane, and forming an edge portion in which the edge of the        sub-assembly is aligned with the edge of the backplane.

This process of the present invention may hereinafter for convenience becalled the “simultaneous trimming” or “ST” process of the invention.

In the ST process, the front sheet may comprise a light-transmissiveelectrically-conductive layer which will form a front electrode in thefinal display, so that the sub-assembly has the form of a FPL orinverted FPL. Also, in such a case, the front sheet will typically alsocomprise at least one supporting or protective layer on the opposed sideof the electrically-conductive layer from the layer of electro-opticmedium, the supporting or protective layer serving to support theelectrically-conductive layer and to protect it against mechanicaldamage. The supporting or protective layer may also serve otherfunctions, for example by acting as a barrier against water vapor and/orultra-violet radiation, and/or providing a desired surface texture. Thesupporting or protective layer may be larger than the layer ofelectro-optic medium (and possibly larger than the adhesive layer) andonly a peripheral portion of the supporting or protective layer may besecured to the backplane, thus forming a seal around the electro-opticmedium. In such a case, the ST process may only require cutting throughthe peripheral portion of the supporting or protective layer and theadjacent portion of the backplane to form the aligned edge portion.

The ST process may be used to do more than simply remove peripheralportions of the sub-assembly and backplane to produce an aligned edge.As described in copending application Ser. Nos. 12/146,063 and12/146,112, both filed Jun. 25, 2008, and as illustrated below, it maybe convenient to provide the sub-assembly with certain auxiliarystructures, for example a tacking strip and an inspection tab, which areuseful in assembly or testing of the display, but which are not desiredin the final product. The trimming of the peripheral portions of thesub-assembly and backplane to produce an aligned edge provides aconvenient opportunity for removal of such auxiliary structures. Thetrimming operation may also conveniently be used to provide mechanicalalignment or attachment points, for example by forming apertures throughthe sub-assembly and backplane.

The electro-optic medium used in the processes of the present inventionmay be any solid electro-optic medium of the types previously described.Thus, the electro-optic medium may be a rotating bichromal member orelectrochromic medium. The electro-optic medium may also be anelectrophoretic material comprising a plurality of electrically chargedparticles disposed in a fluid and capable of moving through the fluidunder the influence of an electric field. The electrically chargedparticles and the fluid may be confined within a plurality of capsulesor microcells. Alternatively, the electrophoretic material may be of thepolymer-dispersed type, with the electrically charged particles and thefluid present as a plurality of discrete droplets surrounded by acontinuous phase comprising a polymeric material. The fluid used may beliquid or gaseous.

This invention extends to the novel sub-assemblies and displays producedby the processes of the present invention. Electro-optic displaysproduced using the methods of the present invention can be used in anyof the applications in which electro-optic displays have previously beenused. Accordingly, this invention extends an electronic book reader,portable computer, tablet computer, cellular telephone, smart card,sign, watch, shelf label or flash drive comprising a display of thepresent invention, or produced using a method or component of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not strictly to scale. In particular, forease of illustration, the thicknesses of the various layers are greatlyexaggerated relative to their lateral dimensions. The present inventionis well adapted for the production of thin, flexible electro-opticdisplays; typically, the sub-assemblies used in the processes describedbelow will have thicknesses of about 100 μm, and can be laminated toflexible backplanes of similar thickness.

FIGS. 1A to 1E are schematic side elevations of various stages in theproduction of a sub-assembly used in a process of the present inventionwhich makes use of both the adhesive layer locating aperture and chip insub-assembly aperture aspects of the invention.

FIGS. 2A and 2B are schematic top plan views at the same stages of theprocess as FIGS. 1D and 1E respectively.

FIG. 3 is a schematic side elevation showing a chip disposed in anaperture in a display formed from the sub-assembly produced in FIGS. 1Ato 1E, 2A and 2B.

FIGS. 4A to 4C are schematic side elevations of various stages in afirst simultaneous trimming process of the present invention, while FIG.4A also illustrates the manner in which the front plane laminate shownin FIGS. 1E and 2B can be laminated to a backplane.

FIG. 5 is a top plan view of the front plane laminate used in theprocess shown in FIGS. 4A to 4C.

FIGS. 6A to 6B are schematic cross-sections illustrating differentstages in a second simultaneous trimming process of the presentinvention.

FIG. 6C is a schematic cross-section, similar to those of FIGS. 6A and6B, through a modified version of the display shown in FIGS. 6A and 6B.

DETAILED DESCRIPTION

As will be apparent from the foregoing Summary of the Invention, thepresent invention has a number of different aspects. However, asillustrated in the preferred embodiments discussed below, a singlephysical electro-optic display or process for the production thereof maymake use of multiple aspects of the present invention. For example, theprocess described below with reference to FIGS. 1A to 1E, 2A and 2B usesboth the ALLA and CSSA aspects of the present invention.

Before describing in detail various embodiments of the present inventionit is useful to set out certain definitions. The term “backplane” isused herein consistent with its conventional meaning in the art ofelectro-optic displays and in the aforementioned patents and publishedapplications, to mean a rigid or flexible material provided with one ormore electrodes. The backplane may also be provided with electronics foraddressing the display, or such electronics may be provided in a unitseparate from the backplane. In flexible displays (and the presentinvention is especially although not exclusively intended for use inflexible displays), it is highly desirable that the backplane providesufficient barrier properties to prevent ingress of moisture and othercontaminants through the non-viewing side of the display. If one or moreadditional layers need to be added to the backplane to reduce ingress ofmoisture and other contaminants, the barrier layers should be located asclosely as possible to the electro-optic layer so that little or no edgeprofile of low barrier materials is present between the front (discussedbelow) and rear barrier layers.

As already indicated, the sub-assembly used in the present processes maycomprise at least one electrode layer, most commonly a single continuousfront electrode extending across the entire display. Typically, thesurface of the sub-assembly which remains exposed after lamination tothe backplane will form the viewing surface through which an observerviews the display. As with the backplane, the sub-assembly may providebarrier properties to prevent ingress of moisture and other contaminantsthrough the viewing side of the display. If one or more additionallayers need to be added to the sub-assembly to reduce ingress ofmoisture and other contaminants, the barrier layers should be located asclosely as possible to the electro-optic layer so that little or no edgeprofile of low barrier materials is present between the front and rearbarrier layers.

Reference will be made hereinafter to “loose” and “tight” releasesheets. These terms are used in their conventional meaning in the art toindicate the magnitude of the force necessary to peel the relevantrelease sheet from the layer with which it is in contact, a tightrelease sheet requiring more force than a loose release sheet. Inparticular, if a stack of layers has a tight release sheet on one sideand a loose release sheet on the other, it is possible to peel the looserelease sheet away from the stack without separating the tight releasesheet from the stack.

Some of the displays and sub-assemblies used in the present inventioncontain two separate adhesive layers. When necessary or desirable, thetwo adhesive layers will be denoted as “front” and “rear” adhesivelayers, these terms denoting the position of the relevant adhesive layerin the final display; the front adhesive layer is the adhesive layerlying between the electro-optic medium and the viewing surface of thedisplay, while the rear adhesive layer lies on the opposed side of theelectro-optic layer from the front adhesive layer. In the commonsituation where a display has a single front electrode between theelectro-optic layer and the viewing surface and a plurality of pixelelectrodes on the opposed side of the electro-optic layer, the frontadhesive layer lies between the electro-optic layer and the frontelectrode, while the rear adhesive layer lies between the electro-opticlayer and the pixel electrodes.

A preferred process which makes use of both the ALLA and CSSA aspects ofthe present invention will now be described with reference to FIGS. 1Ato 1E and 2A to 2B of the accompanying drawings.

FIGS. 1A to 1E are schematic sections through various stages in theproduction of a sub-assembly used in a first process of the presentinvention. In the first step of the process, an electro-optic medium iscoated or otherwise deposited on to a tight release sheet 102 to form anelectro-optic layer 104. Separately, a front adhesive layer 106 iscoated on to a loose release sheet 108. The two resulting sub-assembliesare then laminated to each other with the adhesive layer 106 is contactwith the electro-optic layer 104 to produce the structure shown in FIG.1A. These steps are as described in the aforementioned U.S. Pat. No.7,110,164, and the resulting assembly is a double release sheet asdescribed in the aforementioned 2004/0155857.

In the second step of the process, the structure shown in FIG. 1A iskiss cut with the loose release 108 facing the cutter (typically a lasercutter), the kiss cutting being effected such that the loose releasesheet 108, the front adhesive layer 106 and the electro-optic layer 104are severed but the tight release sheet 102 is not. The continuousportions of the loose release sheet 108, the front adhesive layer 106and the electro-optic layer 104 are then removed, either manually ormechanically, thus leaving the structure shown in FIG. 1B, in whichthere extend upwardly from the tight release sheet 102 multiple “mesas”comprising the islands 208 of the loose release sheet and similarlysized areas 206 and 204 of the front adhesive layer and electro-opticlayer respectively. Each of these mesas will eventually form a separatedisplay. (In some cases, it may be possible to recycle the portions ofthe front adhesive layer and electro-optic layer removed with the looserelease sheet 108 in other small displays.)

The stages of the process described thus far will typically be carriedout either on continuous webs of material, or on large sheets ofmaterial sufficient to form several final displays. For ease ofillustration, FIG. 1B shows only two separate mesas but it will beappreciated that in practice a larger number of mesas will be present ona single large sheet or web. When the process is carried on a web, on aroll-to-roll basis, the webs used may include tractor feed holes formedalong the side edges of the web of material to serve as alignment holes.

In the next step, the remaining portions 208 of the loose release sheetare peeled from the structure shown in FIG. 1B and the remaining layersof the structure are laminated to a sheet of a front substrate 120. Thefront substrate 120 is a multi-layer structure including anindium-tin-oxide (ITO) layer which forms the front electrode of thefinal display. The front substrate may further comprise a removablemasking film, which can be removed before the final display is placed inuse.

The front substrate is designed to provide the front light-transmissiveelectrode for the final display. The front substrate 120 can alsoprovide the necessary mechanical support for this thin and relativelyfragile front electrode. In addition, the front substrate preferablyprovides all necessary water vapor and oxygen barriers, and ultra-violetabsorption properties, desirable to protect certain electro-opticlayers, especially electrophoretic layers. The front substrate may alsoprovide desirable anti-glare properties to the viewing surface of thefinal display. The front substrate 120 serves all of these functionswhile still being thin and flexible enough to enable the formation of afinal display sufficiently flexible to be wound around a mandrel of(say) 15 mm diameter. As already noted, the front substrate includes amasking film; this masking film is provided primarily to increase thethickness of the front substrate so as to facilitate handling of thissubstrate during laminations. In a preferred process, the totalthickness of the front substrate as it remains in the final display(i.e., with the masking film removed) is only about 1 mil (25 μm) andthe masking film is used to add about 2 mil (51 μm) to this thicknessfor ease of handling. The masking film also typically serves to preventscratching or adhesion of dust or debris to an adjacent anti-glare layerduring the laminations. The structure resulting from this step of theprocess is shown in FIG. 1C.

The steps of the process described so far as essentially identical tothose of the process described with reference to FIGS. 2A to 2E of theaforementioned 2008/0057252, to which the reader is referred for furtherinformation.

At this point, a second, thin adhesive layer 122 is coated on to a thirdrelease sheet 124, and apertures 126 are formed though both the adhesivelayer 122 and the release sheet 124 at positions corresponding to wheretop plane connections (connections between the backplanes and the frontelectrodes) will be present in the final displays. At the same time, therelease sheet is cut, preferably discontinuously, along a line 127 (seeFIG. 2A) to form a tacking strip (discussed further below). The releasesheet 102 is peeled from the structure shown in FIG. 1C and the adhesivelayer 122 laminated to the electro-optic layer portions 204 to give thestructure shown in FIG. 1D. FIG. 2A shows a corresponding top plan viewwhich only illustrates a single mesa and its associated aperture 126 andthe line 127; at this stage of the process, the material is still in webor large sheet form and FIG. 2A illustrates only part of the web orsheet, as indicated by the curved boundary of front substrate 120 inFIG. 2A. The adhesive layer 122 must of course be correctly aligned withrespect to the mesas to ensure that the apertures 126 and the line 127are in the proper positions relative to their associated mesa, as shownin FIG. 2A. (For ease of illustration, FIG. 2A shows only a singleaperture 126 associated with the mesa. In practice, it is usuallydesirable to provide two or more apertures 126 associated with each mesaso as to provide redundant top plane connections in each final display,thereby ensuring that each display will still function correctly even ifone of its top plane connections is not correctly formed or becomesdamaged during use.)

The next stage of the process is singulation, that is to say separationof the portions of the sub-assembly corresponding to individualdisplays. The result of this singulation step is illustrated in FIGS. 1Eand 2B. The singulation step simultaneously effects three logicallyseparate operations, namely:

-   -   (a) cutting of the sheet or web into pieces of the size required        for individual displays;    -   (b) formation of apertures through the adhesive layer 122, the        front substrate 120 and the release sheet 124 required for        mechanical alignment of the sub-assembly during subsequent        lamination to a backplane; and    -   (c) formation of an aperture through the front substrate 120,        and the adhesive layer 122, this aperture being ultimately used        to mount an electronic circuit device on the backplane of the        final display.

As illustrated in FIGS. 1E and 2B, operation (a) is effected by cuttingthe front substrate 120, the adhesive layer 122 and the release sheet124 along the same rectangular perimeter, thus defining a separate unit(piece) of front plane laminate which will eventually be laminated to abackplane to form a single display. In addition to the singulation ofthe separate unit of front plane laminate, this step creates an extendedtab or “tail” of non-optically active material (the portion of the frontplane laminate lying below the electro-optic layer 204 as illustrated inFIG. 2B) that adds to the thickness of the corresponding section of thefinal display. Were this tail of non-optically active material notpresent, the thickness of the final display in this region would be onlythe thickness of the backplane itself, and in thin, flexible displays,the thickness of this backplane may be only about 25 μm; the extendedtail section will typically provide an additional 25 μm of thickness,thus doubling the thickness of this region to about 50 μm. See theaforementioned 2007/0211331 for further discussion of providing a tab ortail portion of a front electrode layer, and use of such a tab or tailportion to provide electrical contact with the front electrode layer.

Operation (b) is effected by providing two small circular apertures 128adjacent one edge (the lower edge as illustrated in FIG. 2B) of therectangular front plane laminate. (For ease of comprehension, theapertures 128 are shown in broken lines in FIG. 1E even though FIG. 1Eis a section looking upwardly in FIG. 2B so the apertures 128 would notactually be visible in the section of FIG. 1E.) As shown in FIG. 1E, theapertures 128 lie within the tail section of the FPL and extend throughthe whole thickness of the FPL, passing through the front substrate 120,the adhesive layer 122 and the release sheet 124. The apertures 128 canbe used to facilitate mechanical alignment or attachment of the FPLduring lamination to a backplane or during later stages of manufacture.As described below with reference to FIGS. 4A to 4C, the apertures 128can be used to engage registration pins or similar co-operating membersprovided on the backplane, or on a substrate carrying the backplane, toensure accurate registration of the FPL with respect to the backplane.The apertures 128 can also be used in later stages of the manufacturingprocess to locate the final display module accurately with respect to ahousing or other surrounding portion (for example, a printed circuitboard) of the final commercial display unit, or to attach the displaymodule to such housing or surrounding portion.

Operation (c) is effected by providing a rectangular aperture 130 in thetail portion of the FPL, this rectangular aperture 130 extendingcompletely through the FPL, i.e., through the front substrate 120, theadhesive layer 122 and the release sheet 124. As discussed below withreference to the ST process of the present invention, the type of FPLshown in FIGS. 1E and 2B is typically used with a backplane which isessentially the same size as the FPL, so that the FPL covers essentiallythe whole of the backplane. Accordingly, if it is desired to haveelectrical access to the backplane, for example for mounting driverchips on the backplane, an aperture must be formed to permit this, andthis is the function of the aperture 130. Driver chips or otherelectronic circuit devices can be placed within the aperture 130, andthe FPL surrounding the aperture provides a region of increasedthickness which assists ruggedization of the display.

As also illustrated in FIG. 2B, the singulation of the FPL piece fromthe web results in the line 127 extending close to and parallel to oneedge of the FPL piece, so that between the line 127 and the adjacentedge is formed a tacking strip 129, in the form of an elongate arearunning along one edge of the FPL piece. Because the release sheet 124is severed along line 127, the section of the release sheet 124underlying the tacking strip 129 can be removed without removing therelease sheet 124 from the main part of the FPL piece. The tacking strip129 is provided to assist in locating the FPL piece on a backplane priorto the lamination of these two parts to form a display; the section ofthe release sheet 124 underlying the tacking strip 129 is removed andthe portion of the adhesive layer 122 thus exposed can be pressedmanually into the correct position for lamination to the backplane,before the main portion of the release sheet 124 is removed and thelamination operation completed.

FIG. 3 of the accompanying drawings is a highly schematic side elevationof a driver die 144 disposed within an aperture (designated 130′) of adisplay formed by laminating a front plane laminate 140 to a backplane142. As shown in FIG. 3, the driver die 144 extends through the aperture130′ and makes electrical contact with contacts (not shown) present onthe backplane 142. A potting material 146 surrounds the die 144 andcontacts portions of the FPL 140 surrounding the aperture 130′, thispotting material 146 serving to protect the drive contacts fromenvironmental factors and to mechanically stabilize the interconnectionbetween the die 144 and the backplane 142.

FIG. 4A illustrates, in a highly schematic manner, a process in whichthe piece of front plane laminate shown in FIGS. 1E and 2B is laminatedto a backplane. As shown in FIG. 4A, a support table 150 is providedwith a pair of pins 152 (only one of which is visible in FIG. 4A). Abackplane 154 is provided with apertures which engage the pins 152. Therelease sheet 124 (see FIG. 1E) is removed from the front plane laminate156, which is then laid over the backplane with the apertures 128 (seeFIGS. 1E and 2B) engaged with the pins 152. A roller 158 passes over thefront plane laminate 156, thus adhering the adhesive layer 122 (see FIG.1E) to the adjacent surface of the backplane 154 and thus laminating thefront plane laminate to the backplane to form a display. Following thislamination, the laminated FPL and backplane are removed from the supporttable 150 as the structure shown in FIG. 4B. (The meaning of the arrowsin FIG. 4B will be explained below with reference to the ST process ofthe present invention.)

Detailed consideration will now be given to the simultaneous trimming(ST) process of the present invention. As noted above, when laminatingfront plane laminates to a backplane, the FPL must typically be alignedwith respect to backplane features, for example contact pads designed toprovide contacts to the electrode layer present in the front planelaminate. Depending on the design requirements, the FPL can be designedto be smaller than the backplane (to allow access to electricalconnections on areas of the backplane not covered by the FPL) or thesame size as the backplane. If the FPL, or a barrier layer laminatedover the FPL, is the same size as the backplane, achieving a clean edgealignment can be difficult in practice, since there is always sometendency for the FPL not to line up exactly with the backplane. Also,certain features desirable during manufacture, such as inspection tabsor tacking strips, can be undesirable if present in the finished displaymodule.

There is an increasing tendency to use electro-optic media with thinbackplanes based on polymeric films (for example, poly(ethyleneterephthalate) or poly(ethylene naphthalate), PEN, availablecommercially under the Registered Trade Mark TEONEX from DuPont TeijinFilms of Hopewell Va.) or metal foils. Electro-optic displays based onsuch thin backplanes can be flexible or rollable and hence usable incertain applications (for example, a large display screen capable ofbeing stored in a cellular telephone—see the aforementioned2002/0090980) where traditional displays cannot be used. It has now beenfound that, using the simultaneous trimming process of the presentinvention, an FPL laminated to such a polymeric or metal foil backplanecan readily be cut by industrial methods, for example laser cutting ordie cutting, and that such cutting of an FPL/backplane laminate enablesan accurately matched edge to be achieved between the FPL (or a barrierlayer overlying the FPL) and the backplane, without adverse effects onthe functionality of the final display. Such cutting also allows for theremoval of features useful during manufacture but not wanted in thefinal display.

A preferred simultaneous trimming process of the present invention willnow be described with reference to FIGS. 4A to 4C and 5. FIG. 5 shows afront plane laminate which is generally similar to that shown in FIG.2B. In FIG. 5, the electro-optic layer 204, the adhesive layer 206, andthe apertures 126 and 130 differ in size and position from thecorresponding integers in FIG. 2B but are otherwise similar and servethe same functions. However, the front plane laminate shown in FIG. 5has a number of additional features. These features include a top planecontact tab 160, which is used to make electrical contact with theelectrode layer of the FPL during testing, a release contact tab 162which is similarly used to make electrical contact with a conductivelayer provided in the release sheet 124 for testing purposes (see thetesting methods described in the aforementioned U.S. Pat. No. 6,982,178)and a tacking strip 164. The tacking strip 164 is constructed in thesame manner as, and functions in the same way as, the tacking strip 129described above with reference to FIGS. 2A and 2B.

The FPL shown in FIG. 5 is designed to be laminated to a backplanehaving transistors on a thin plastic film, for example a PEN film. Thelamination of the FPL to the PEN film backplane is effected in themanner shown in FIGS. 4A and 4B, as previously described. The resultinglaminate is then trimmed by laser cutting (die cutting couldalternatively be used), as indicated schematically by the arrows in FIG.4B and along the periphery indicated by the broken line in FIG. 5 toproduce the final display module, illustrated schematically in FIG. 4C.This trimming operation removes the contact tabs 160 and 162, and thetacking strip 164. Apertures for mechanical alignment or for attachmentpoints can be incorporated into the display during the trimmingoperation. Such apertures may be useful, for example, for securing thedisplay to fixtures, or for optical alignment, during latermanufacturing operations or for securing the display to a displayhousing.

In the simultaneous trimming process shown in FIGS. 4A to 4C and 5, thefront substrate of the FPL acts as a barrier layer protecting theelectro-optic layer from environmental contaminants and radiation.However, as described for example in the aforementioned U.S. Pat. No.6,982,178 (see especially FIGS. 18-20 and the related description),electro-optic display can be produced having a barrier layer which isseparate from the front substrate of the display, with an edge sealformed between the barrier layer and the backplane. The ST process ofthe present invention can also be applied to this type of display, and apreferred process of this type is illustrated in FIGS. 6A and 6B.

FIG. 6A illustrate a barrier-layer-protected display (generallydesignated 600) of the type shown in FIG. 3 of the aforementioned2007/0152956. The display 600 comprises a backplane 602, an adhesivelayer 122, an electro-optic layer 204 (illustrated as an encapsulatedelectrophoretic layer in FIG. 6A), a front substrate 120 and a barrierlayer 622. A peripheral portion 622P of the barrier layer 622 is crimpedaround the periphery of the electro-optic layer 204 and sealed, eitheradhesively or, depending upon the materials used, in some cases bywelding, to the peripheral part of the backplane 602 to form an edgeseal which seals the electro-optic layer 204 from outside contaminants.

It will be seen from FIG. 6A that the barrier layer 622 is slightlysmaller than the backplane 602; in practice, with this type of edge sealit is very difficult to keep the edges of the barrier layer and thebackplane closely aligned. In accordance with the ST process of thepresent invention, the structure shown in FIG. 6A can be cut, asindicated by the arrows in that Figure, to produce the structure shownin FIG. 6B, in which the edges of the barrier layer and backplane arealigned.

The ST process shown in FIGS. 6A and 6B only cuts through the barrierlayer and the backplane. Other ST processes may require cutting throughthe barrier layer, the backplane, and one or more of the electro-opticlayer, adhesive layers and front substrate. FIG. 6C shows a modifieddisplay (generally designated 650) generally similar to the display ofFIG. 6B but having an aperture 624 extending through a peripheralportion thereof. The display 650 of FIG. 6C is produced from theuntrimmed display 600 shown in FIG. 6A, and the left-hand side of thedisplay 600 (as illustrated in FIG. 6A) is trimmed in the same way as inFIG. 6B to provide a trimmed edge. However, the right-hand edge ofdisplay 600 is not trimmed but instead a punch (not shown) is used toform the aperture 624 extending through the display 650.

It will be apparent to those skilled in the technology of electro-opticdisplays that numerous changes and modifications can be made in thepreferred embodiments of the present invention already described withoutdeparting from the scope of the invention. For example, in the preferredprocesses of the invention illustrated in the drawings, the invertedfront plane laminate is cut into pieces of the size required for anindividual display (see FIGS. 1E and 2B) before being laminated to abackplane. When high volume production is desired, it may be convenientto reverse the order of these singulation and lamination operations,i.e., a sheet or web of inverted front plane laminate sufficient to forma plurality of displays could be laminated in an aligned manner to asheet or web of backplanes to form a plurality of displays which arethereafter singulated from the sheet. When the lamination operation isperformed on sheets, the sheet of backplanes will typically be held on asupport member during the lamination, and the singulation operation canbe effected with the sheet of displays still held on the support member.Such a process permits singulation of the displays and the ST process ofthe present invention to be effected in a single operation.

Furthermore, although the invention has been shown in FIGS. 6A and 6Bapplied to an edge seal formed by sealing a protective layer to abackplane, the present invention can be used with a variety of othertypes of edge seals. In particular, the aforementioned U.S. Pat. No.6,982,178 describes several different types of so-called “underfill edgeseals” in which peripheral portions of a backplane, and either a frontsubstrate or a protective layer overlying a front substrate, extendoutwardly beyond the periphery of an electro-optic layer, and an edgeseal is formed extending between the peripheral areas of the backplaneand either the front substrate or the protective layer. The simultaneoustrimming process, and the other processes of the present invention, canbe applied to displays having such underfill edge seals either before orafter the edge sealing material is applied. Similarly, although theprocesses of the present invention have primarily been described abovewith reference to displays constructed using inverted front planelaminates, these processes can also be used with displays using“classic” front plane laminates, double release films and othersub-assemblies.

Numerous other variations of the processes of the present invention willreadily be apparent to those skilled in the technology of electro-opticdisplays. Accordingly, the whole of the foregoing description is to beconstrued in an illustrative and not in a limitative sense.

1. A process for the production of an electro-optic display, the processcomprising: forming a sub-assembly comprising in order, a front sheet; alayer of electro-optic medium; and an adhesive layer; securing thesub-assembly to a backplane comprising at least one pixel electrode; andcutting through both the sub-assembly and the backplane, therebyremoving peripheral portions of both the sub-assembly and the backplane,and forming an edge portion in which the edge of the sub-assembly isaligned with the edge of the backplane.
 2. A process according to claim1 wherein the front sheet comprises a light-transmissiveelectrically-conductive layer.
 3. A process according to claim 2 whereinthe front sheet also comprises at least one supporting or protectivelayer on the opposed side of the electrically-conductive layer from thelayer of electro-optic medium, the supporting or protective layerserving to support the electrically-conductive layer and to protect itagainst mechanical damage.
 4. A process according to claim 3 wherein thesupporting or protective layer is larger than the layer of electro-opticmedium and only a peripheral portion of the supporting or protectivelayer is secured to the backplane, thereby forming a seal around thelayer of electro-optic medium.
 5. A process according to claim 4 whereinthe cutting through the sub-assembly and the backplane is effected bycutting only through the supporting or protective layer and the adjacentportion of the backplane.
 6. A process according to claim 1 wherein theelectro-optic material comprises a rotating bichromal member orelectrochromic material.
 7. A process according to claim 1 wherein theelectro-optic material comprises an electrophoretic material comprisinga plurality of electrically charged particles disposed in a fluid andcapable of moving through the fluid under the influence of an electricfield.
 8. A process according to claim 7 wherein the electricallycharged particles and the fluid are confined within a plurality ofcapsules or microcells.
 9. A process according to claim 7 wherein theelectrically charged particles and the fluid are present as a pluralityof discrete droplets surrounded by a continuous phase comprising apolymeric material.
 10. A process according to claim 7 wherein the fluidis gaseous.
 11. A process according to claim 1 wherein the cutting stepalso effects at least one of: (a) removal of at least one contact tabfrom the sub-assembly; (b) removal of at least one tacking strip fromthe sub-assembly; and (c) formation of at least one aperture through thedisplay.